This invention relates to the field of COMINT/ELINT (communications intelligence/electronic intelligence) signal processing, and more particularly to signal detection of low-level BPSK (binary phase shift keying) signals, and location of those signals by using a dual-channel chirp-Z interferometer processor to measure the phase relationship of signals received at a plurality of antennas.
A system of background interest is disclosed in U.S. Pat. No. 4,443,801 entitled, "Direction Finding and Frequency Identification Method and Apparatus" by D. Klose and W. Skudera, Jr. dated Apr. 17, 1984 ("the '801 patent"). The disclosures of this and all other prior art materials mentioned herein are expressly incorporated by reference. This patent describes a system wherein frequency and AOA measurements can be accurately obtained on primarily CW-type multiple-intercept signals by utilizing a dual channel chirp-Z processor. For convenience, a diagram showing relevant details of the '801 patent is given in FIG. 1.
A standard interferometer processor cannot do direction-finding (DF) on low-level BPSK signals because such signals have numerous phase changes that flip between zero and 180 degrees, which introduces measurement errors in the angle-of-arrival (AOA) and subsequent signal location. Another problem is that the chirp-Z transform of the BPSK signal is spread out with a small correlation peak and, therefore, is more difficult to detect when the input signal strength is of a low level.